Microbiology & Immunology

Question 1

What are the symptoms of Blepharitis? List at least 5)

Answer 1

Burning, flaking, tearing, crusting, tearing, irritation, itching, *redness in the eyelid margin, *foreign body sensation, * scales similar to dandruff forming at the base of the eyelashes

Question 2

Types of Blepharitis and their common causes.

Answer 2

Anterior Blepharitis: associated with a mite infection (Demodex folliculorum), seborrhoeic dermatitis (dandruff), Staphylococcus aureus or a mixed infection of S. aureus and S. epidermidis and Propionibacterium
Posterior Blepharitis: Meibomian seborrhoea, Meibomianitis - excess production of oil by the gland

Question 3

Possible outcome of Anterior Blepharitis without treatment

Answer 3

if severe, can include ectropion, trichiasis and entropion

Question 4

Staphylococcal blepharitis management (anterior)

Answer 4

Requires good eyelid hygiene to remove debris, warm compressions and artificial tears.
Antibiotic ointment (framycetin, tetracycline or chloramphenicol) until clinically resolved
Condition may never be “cured” or permanently relieved.

Question 5

What is (External) Hordeolum (Stye)?

Answer 5

An acute localised swelling of the eyelid - typically obstruction or infection of the eyelash follicle.
Usually associate with staphylococcal infection

Question 6

Symptoms of Hordeolum (external)

Answer 6

Painful and remains localised to an eyelid margin.

Pyogenic (pus)

Question 7

Treatment of hordeolum (External)

Answer 7

Treat with hot compressions; sometimes drainage

Question 8

What is (internal) Hordeolum?

Answer 8

Result from an ifnection of the Meibomian gland (“internal stye” or Meibomian abscess).
Associated with staphylococci

Question 9

Symptoms of hordeolum (internal)

Answer 9

Tender, usually discharges spontaneously

Question 10

Treatment of hordeolum (internal)

Answer 10

Warm compresses and oral anti-staphylococcal antibiotics (flucloxavillin/cephalexin) - particularly if there is cellulitis
Persistent or recurrent infections may need surgery

Question 11

What is Chalazion?

Answer 11

It is an inflammation of a blocked meibomian gland (NOT infection)

Question 12

Symptoms of chalazion?

Answer 12

Usually located on the upper eyelid on the inside of the lid, painless, subacute

Question 13

Treatment of chalazion?

Answer 13

Warm compressions (to soften hardened oil) - don't squeeze or pop
Often disappears without treatment, however may need corticosteroid injections or surgical removal for larger ones

Question 14

Characteristics of Staphylococci

Answer 14

Gram stain: +ve cocci
Size: 1 micron in diameter
Population: typically in clusters in a stained smear
Media: simple media NA
Metabolism: Facultative anaerobes (grow both aerobically and anaerobically)
Other: pyogenic bacteria (pus production - pus = liquid containing the remains of dead leucocytes, pathogens and decomposed cellular debris)
Tolerate bile salts
May produce pigemented colonies
Catalase positive
Major pathogen: S. aureus (coagulase positive
Opportunistic pathogen: S. epidermidis (coagulase negative
Both grow rapidly on basic media

Question 15

Ocular infections of Staphylococci

Answer 15

S. aureus: important cause of blepharitis, keratitis, meibomianitis, endophthalmitis, preseptal cellulitis, ‘sterile corneal ulcer’, CNPU and conjuctivitis
S. epidermidis: a major cause of endophthalmitis (especially post-op)

Question 16

How do Staphylococci cause disease? (pathogenesis)

Answer 16

Staphylococci are hardy and can survive well in environment. They can survive drying.
It induces acute inflammatory reaction (complement cascade triggered by cell wall components) –> abscess formation (aided by coagulase production)
It evides phagocyte action (e.g. catalase, leucocidin, protein A - binds Ig)
“Golden Staph” S. aureus: > dozens of possible adhesins for colonisation
Also contain many virulence factors that cause damage and allow spread (e.g. toxins: haemolysins, exfoliative toxin, enterotoxin & enzymes: hyaluronidase, lipase, proteases, DNases)